The present invention relates to a semiconductor device and a method for producing the same. In particular, the invention relates to a semiconductor device which is flexibly adapted to a circuit wiring pattern on the printed circuit board for mounting the semiconductor device, and a method for producing this semiconductor device.
FIG. 4(a) is a plan view showing typical conventional semiconductor devices. Each semiconductor device is composed of a semiconductor die 1, and a lead frame 7 equipped with a die paddle 2 for mounting the semiconductor die 1 and four lead terminals 3, 4, 5, 6 for external connections. The die paddle 2 is joined with and supported by the lead terminal 4. This die paddle 2 and portions of the lead terminals 3, 4, 5, 6 are encapsulated in a plastic package 8.
In the lead frame 7, the lead terminals 3, 4, 5, 6 are tied together at the middle by a tie bar 11, with one end of each lead terminal being joined with and supported by a cross rail 9. The cross rail 9 holds a plurality of lead frames 7 side by side. In each lead frame 7, one end of the die paddle 2 is joined with and supported by the cross rail 9 via the lead terminal 4, and the other end of the die paddle 2 is joined with and supported by another cross rail 10. Similarly, the cross rail 10 holds the lead frames 7 side by side.
FIG. 4(b) is a plan view showing a different type of conventional semiconductor devices. In each semiconductor device shown in FIG. 4(b), the die paddle 2 is joined with and supported by the cross rail 9 via the terminal lead 5, not via the terminal lead 4 as in the semiconductor devices of FIG. 4(a).
A method for producing the conventional semiconductor devices shown in FIG. 4(a) is described with reference to FIG. 5 and FIG. 6.
To start with, a semiconductor die 1 is bonded to the die paddle 2 in each lead frame 7 (see FIG. 5).
Next, the semiconductor die 1 is connected to the lead terminals 3, 5, 6 and the die paddle 2 by bonding wires 12 in order to form a circuit. The reverse face of the semiconductor die 1 is also electrically connected to the die paddle 2.
Then, the lead frame 7 is encapsulated in a plastic package 8 by transfer molding, etc. Finally, the cross rails 9, 10 and the tie bar 11 are cut off to give a semiconductor device (see FIG. 6).
A production line for these conventional semiconductor devices is shown by the flowchart in FIG. 7. The production line proceeds continuously from the lead frame manufacture step, to the semiconductor die bonding step, to the wire bonding step, to the plastic encapsulation step, and ends with the tie bar cutting step. This production line is individually set up for lead frames of every shape. For example, since the shapes of lead frames 7 are different between the semiconductor devices shown in FIG. 4(a) and FIG. 4(b), these devices adopt individual specifications (dies, etc.) in the lead frame manufacture step. The difference in the lead frame shape necessitates modification of specifications not only in the lead frame manufacture step, but also in the semiconductor die bonding step, the wire bonding step, the plastic encapsulation step, and the tie bar cutting step. Eventually, there should be as many production lines as the shapes of lead frames.
This issue is discussed in more detail. FIG. 8 illustrates how a conventional semiconductor device is mounted on a printed circuit board. Taking the semiconductor device shown in FIG. 4(a) as an example, the lead frame 7 is equipped with the lead terminal 3 as an input voltage terminal, the lead terminal 4 as an output voltage terminal, the lead terminal 5 as a GND terminal, and the lead terminal 6 as an output voltage control terminal. In order to mount this semiconductor device on a printed circuit board 13, the circuit wiring on the printed circuit board 13 needs to be adapted to the lead terminal arrangement in the semiconductor device, as illustrated in FIG. 8. Thus, a printed circuit board has to be designed to the lead terminal arrangement in the semiconductor device.
Alternatively, the terminal arrangement in the semiconductor device may be altered to match the circuit wiring on the circuit board. For example, where the output voltage terminal and the GND terminal need to be changed merely between each other (specifically speaking, where it is necessary to turn the lead terminal 4 into a GND terminal and the lead terminal 5 into an output voltage terminal), another semiconductor device has to be produced with use of the lead frame 7 shown in FIG. 4(b). Since the lead frames 7 of FIG. 4(a) and FIG. 4(b) are different in shape, an additional production line should be set up for the latter lead frame 7. In this case, too, there should be as many production lines as the shapes of lead frames.
Apart from these disadvantages, the conventional semiconductor device suffers from other problems. In one respect, the die paddle 2 may bend during in-line transfer or the like in the production of the semiconductor device, in which case the die paddle 2 causes troubles in the production process. Therefore, before the production of the conventional semiconductor device, the lead frame 7 is constructed to prevent bending of the die paddle 2, with the die paddle 2 being joined with and supported by the cross rail 10 in advance. In another respect, from the viewpoint of reducing the material cost for the lead frame 7, it is necessary to minimize extra portions which are cut off in the tie bar cutting step. This requirement leads to a lead frame 7 which omits the cross rail 10, the most part of which is eventually removed. Nevertheless, if the cross rail 10 is omitted in the lead frame 7 of FIG. 4(a), the die paddle 2 is supported by the lead terminal 4 alone and shows a less strength against bending. As mentioned above, the conventional semiconductor devices are confronted with the difficulty in maintaining the strength of lead frames as well as reducing the material cost therefor.
In order to solve these problems, the present invention aims to provide a semiconductor device which enables efficient rearrangement of lead terminals, which maintains the strength of a die paddle during the production process as well as reduces the material cost for a lead frame, and which is obtained by a single production line. The invention also aims to provide a method for producing this semiconductor device.
In order to achieve the above objects, a semiconductor device according to the invention comprises a semiconductor die, and a lead frame equipped with a die paddle for mounting the semiconductor die and a plurality of lead terminals for external connections, the die paddle and die paddle-side ends of the lead terminals being encapsulated together in a plastic package. In this semiconductor device, the die paddle is provided with a plurality of links which extend one by one between the lead terminals, with an extreme end of each link being integrated with adjacent lead terminals. The semiconductor die is electrically connected to part of the lead terminals which correspond to a wiring pattern of an external circuit, and any link uninvolved in such electrical connections is cut off.
According to this invention, the die paddle is provided with the links which extend one by one between the lead terminals, with an extreme end of each link being integrated with adjacent lead terminals. Hence, the die paddle can maintain a sufficient strength to resist bending during the production of a semiconductor device, without resorting to a cross rail which is joined with the die paddle as a support. Besides, the semiconductor die is electrically connected to part of the lead terminals which correspond to a wiring pattern of an external circuit, and any link uninvolved in the electrical connections is cut off. As a result, it is possible to provide a semiconductor device whose terminal arrangement is adaptable to the circuit wiring on the printed circuit board.
In this semiconductor device, the links and the lead terminals may be integrated via a tie bar which ties the lead terminals.
This feature can materialize a lead frame in a simple structure. Also, the die paddle can maintain a sufficient strength to resist bending during the production of a semiconductor device, without resorting to a cross rail which is joined with the die paddle as a support.
In the above semiconductor device, the links and the lead terminals may be integrated outside of the plastic package.
According to this feature, the links and the lead terminals are integrated outside of the plastic package, so that any link can be cut off after the plastic encapsulation.
The present invention also provides a method for producing the above semiconductor device, which comprises the steps of: manufacturing the lead frame which is equipped with a die paddle for mounting a semiconductor die and a plurality of lead terminals for external connections, the die paddle being provided with a plurality of links which extend one by one between the lead terminals, with an extreme end of each link being integrated with adjacent lead terminals (the lead frame manufacture step); attaching the semiconductor die on the die paddle by bonding (the semiconductor die bonding step); electrically connecting the semiconductor die, by wire bonding, to part of the lead terminals which correspond to a wiring pattern of an external circuit board for mounting the semiconductor device (the wire bonding step); encapsulating the die paddle and die paddle-side ends of the lead terminals together in a plastic package (the plastic encapsulation step); and cutting off the tie bar and the links at a part uninvolved in any such electrical connections (the tie bar/link cutting step).
According to this semiconductor device production method, the tie bar/link cutting step allows simultaneous removal of the tie bar and the links at a part uninvolved in the above electrical connections. In this case, all lead frames can be manufactured in an identical shape in the lead frame manufacture step and can be processed in the same shape until the tie bar/link cutting step. Then, these uniform lead frames undergo the tie bar/link cutting step for removing any link uninvolved in the above electrical connections, so that the lead frames can be individually shaped and adapted to a variety of circuit wiring patterns. Thus, semiconductor devices with different terminal arrangements can be also produced in a single production line.
In the method for producing a semiconductor device according to the present invention, the tie bar/link cutting step may be carried out after the plastic package is formed in the plastic encapsulation step.
This feature can protect the bonding wires from being severed, deformed or damaged otherwise by the link cutting die, so that the bonding wires can ensure electrical connections between the lead terminals and the semiconductor die.